PostgreSQL 遍歷表的PLSQL列舉

我們經常會對數據字典中的系統表進行遍歷，從而寫一些SHELL腳本或者動態造數據等等。 這裏我用PLSQL演示了三種方法來遍歷一張表。  


表結構如下，

t_girl=# \d tmp_1;
           Unlogged table "public.tmp_1"
  Column  |            Type             | Modifiers 
----------+-----------------------------+-----------
 id       | integer                     | 
 log_time | timestamp without time zone | 

在這裏我創建裏一個自定義類型來保存我的函數返回值。

 create type ytt_record as (id int,log_time timestamp without time zone);

 
 現在來看第一個函數。 也是用最笨的方法來遍歷。

create or replace function sp_test_record1(
IN f_id int
) returns setof ytt_record as
$ytt$
declare i int;
declare cnt int;


declare o_out ytt_record;
begin
   i := 0;
   cnt := 0;
   select count(*)   into  cnt from tmp_1 where id > f_id;
   while i < cnt 
   loop
 
       select id,log_time into strict o_out from tmp_1 where id > f_id order by log_time desc limit 1 offset i;
  
     i := i + 1;
     return next o_out;
   end loop;
end;
$ytt$ language plpgsql;

我們來執行下結果，花費了3毫秒左右。

t_girl=# select  * from sp_test_record1(60);
 id |          log_time          
----+----------------------------
 85 | 2014-01-11 17:52:11.696354
 73 | 2014-01-09 17:52:11.696354
 77 | 2014-01-04 17:52:11.696354
 80 | 2014-01-03 17:52:11.696354
 76 | 2014-01-02 17:52:11.696354
 65 | 2013-12-31 17:52:11.696354
 80 | 2013-12-30 17:52:11.098336
 85 | 2013-12-27 17:52:11.098336
 97 | 2013-12-26 17:52:11.696354
 94 | 2013-12-24 17:52:09.321394
(10 rows)


Time: 3.338 ms

現在來看第二個函數，這個就比較優化了， 用了系統自帶的循環遍歷結構。

create or replace function sp_test_record2(
IN f_id int
) returns setof ytt_record as
$ytt$


declare o_out ytt_record;
begin


  for o_out in   select id,log_time  from tmp_1 where id > f_id order by log_time desc 
  loop
     return next o_out;
   end loop;
end;
$ytt$ language plpgsql;

這次運行結果看看，時間不到1毫秒。

t_girl=# select * from sp_test_record2(60);
 id |          log_time          
----+----------------------------
 85 | 2014-01-11 17:52:11.696354
 73 | 2014-01-09 17:52:11.696354
 77 | 2014-01-04 17:52:11.696354
 80 | 2014-01-03 17:52:11.696354
 76 | 2014-01-02 17:52:11.696354
 65 | 2013-12-31 17:52:11.696354
 80 | 2013-12-30 17:52:11.098336
 85 | 2013-12-27 17:52:11.098336
 97 | 2013-12-26 17:52:11.696354
 94 | 2013-12-24 17:52:09.321394
(10 rows)


Time: 0.660 ms

最後一個函數， 利用RETURN QUERY 直接返回結果集。

create or replace function sp_test_record3(
IN f_id int
) returns setof ytt_record as
$ytt$


begin
  return query select id,log_time  from tmp_1 where id > f_id order by log_time desc ;
end;
$ytt$ language plpgsql;

這個結果其實等同於直接從表SELECT，響應時間和第二個差不多。

t_girl=# select sp_test_record3(60);
          sp_test_record3          
-----------------------------------
 (85,"2014-01-11 17:52:11.696354")
 (73,"2014-01-09 17:52:11.696354")
 (77,"2014-01-04 17:52:11.696354")
 (80,"2014-01-03 17:52:11.696354")
 (76,"2014-01-02 17:52:11.696354")
 (65,"2013-12-31 17:52:11.696354")
 (80,"2013-12-30 17:52:11.098336")
 (85,"2013-12-27 17:52:11.098336")
 (97,"2013-12-26 17:52:11.696354")
 (94,"2013-12-24 17:52:09.321394")
(10 rows)


Time: 0.877 ms
t_girl=#